1. Field of the Invention
The present invention relates to an image forming apparatus for forming a toner image on a photosensitive member, and transferring the toner image to a transporting belt or a recording material borne on the transporting belt to thereby obtain an image.
2. Description of Related Art
There have heretofore been proposed various image forming apparatuses which are provided with a plurality of image forming portions, wherein toner images of different colors are formed in the respective image forming portions, and the toner images then are sequentially superimposed and transferred onto the same recording material to thereby form a color image. For high-speed recording, use is made of a color copier of the multi-color electrophotographic type using an endless transfer belt.
There also have been proposed various image forming apparatuses of the intermediate transfer type, in which toner images first are transferred onto an intermediate transfer member, and thereafter are transferred to a transfer material to thereby form a color image.
Among these image forming apparatuses, there is one using as the transfer belt a sheet of polycarbonate or the like having its opposite ends connected together to form an endless belt. In such a product, the long-term use thereof causes the seam to break.
Recently, however, seamless transfer belts have come to be manufactured and the lengthening of their service life has been advanced.
However, with the lengthening of the service life of the transporting belt in the aforedescribed image forming apparatus according to the conventional art, a change in the surface state of the transporting belt due to the long-term use thereof has become remarkable. As causes thereof, mention may be made of, for example, the filming phenomenon that occurs when toners are secured to the surface of the transporting belt, and the fact that the surface of the transporting belt is abraded by a cleaning member or the like abutting against the transporting belt. A change in the surface state occurs not only to the outer surface of the transporting belt (i.e., the surface on which toner images or the transfer material is borne), but also to the inner surface thereof (i.e., the surface contacted by a driving roller for driving the transporting belt).
The coefficient of friction of the transporting belt and the driving roller is changed by such a change in the surface state. Slight slippage is caused during the movement of the transporting belt, and the moving speed thereof becomes unstable. Thereby, deviations occur in the transferred positions of the toner images. Particularly, in the case of a tandem type image forming apparatus provided with multiple sets of photosensitive members for the respective colors of the toners, if the moving speed of the transporting belt is unstable, toner images of the respective colors are not correctly superimposed one upon another, with a result that so-called color misregistration occurs and the quality of image is remarkably deteriorated.
As the endurance change further progresses, the transporting belt becomes incapable of being driven. Also, when the volume resistivity of the transporting belt is changed by the filming phenomenon of the toners on the inner surface of the transporting belt, it will present itself as an uneven image and a good image cannot be obtained.
The present invention has been made in view of the above-noted problem and the object thereof is to provide an image forming apparatus in which slippage of a transporting belt relative to driving means due to a change in the surface state of the inner surface of the transporting belt, and resultant bad images, can be reliably prevented.
In order to achieve the above object, in an image forming apparatus having a photosensitive member on the surface of which a toner image is to be formed, a transporting belt and driving means for driving the transporting belt, and wherein a toner image formed on the surface of the photosensitive member is to be transferred onto the transporting belt or a recording material borne on the transporting belt, abrading means is provided at a position in contact with a surface on which the driving means abuts against the transporting belt.
Provision may be made of detecting means for detecting the surface roughness of the surface of the transporting belt against which the driving means abuts, and the abrading means may be operated on the basis of the result of the detection by the detecting means.
The abrading means may be comprised of an abrading roller.
The abrading means may be comprised of a brush.
The abrading means may preferably operate so that the surface roughness of the transporting belt may be maintained within such a range that a ten-point mean roughness Rz is 3 to 25 xcexcm.